New sim, testing tools used to design Mars lander

WASHINGTON – When engineers at NASA’s Jet Propulsion Laboratory (JPL) realized they had to start from scratch in order to safely land a Mini Cooper-sized rover on the surface of Mars, they realized simulating the fiery descent and landing widely known as the “Seven Minutes of Terror” would require an unprecedented amount of computer simulations and testing.

They turned to companies like Siemens PLM Software to help conduct thermal design and analysis studies to determine how the Mars Science Laboratory spacecraft carrying the Curiosity rover would behave as it descended through the thin Martian atmosphere made up mostly of carbon dioxide and sulfur dioxide. NASA engineers had to figure out how to protect the spacecraft moving at speeds as high as 13,000 miles per hour as it descends to its landing site from temperatures as high as 1,447 degrees C.

If the spacecraft survives the fiery entry into Mars’ atmosphere and its sky crane successfully lands Curiosity on the surface early Monday morning (Aug. 6), the rover must then be able to operate at temperatures ranging from -135 degree C to +50 degrees C.

Tim Nichols, managing director of Siemens PLM Software (PLM stands for Product Lifecycle Management) said in an interview that program managers also had to find ways to model the G forces on the spacecraft during entry, descent and landing. Early in the risky program, Nichols continued, JPL engineers realized they needed a far more integrated approach to simulating the hazardous automated landing and the spacecraft’s predicted behavior as a way to minimize risk.

Click on image to enlarge.

The automated entry, descent and landing sequence of the Mars Science Laboratory spacecraft that will use a risky sky crane landing technique to lower the Curiosity rover to the surface of Mars. (Source: NASA Jet Propulsion Laboratory)

“We provided the toolbox for designing, testing and ultimately manufacturing this robot,” Siegfried Russwurm, CEO of Siemen’s Industry Sector, said during the recent Farnborough Air Show. “Our virtual testing was really used to do things where you would not have a physical prototype” of the spacecraft or rover.

The company claims its integrated suite of tools called NX pulled together disperate CAD, CAE and CAM tools to allow JPL engineers to “capture all of the DNA of [the Mars Science Laboratory] design” and determine, for instance, whether they “over-designed it,” Nichols said. NX was used to develop many of the mechanical portions of the Mars Science Laboratory spacecraft, particularly the thermal control systems for entry, descent and landing as well as for surface operations at Curiosity’s planned landing site at Gale Crater.

The integrated approach allowed JPL engineers to “refine, refine, refine” a never-before-attempted spacecraft design, Nichols said. Among the factors engineers had to take into account in their design were thermal loads and the effects of radiation exposure after the nine-month, 354 million mile trip to Mars.

Doug McCuistion, director of NASA’s Mars Exploration Program, credited the Siemens software with helping engineers manage the evolving design of spacecraft systems. “It was very useful to be able to test the parts and test the interfaces before we had to actually assemble” the spacecraft, he said at Farnborough.

Despite the extensive simulations and testing, program officials acknowledge there is only so much risk that can be eliminated when attempting a fully automated landing of a roughly 1-ton rover on Mars using an untried landing technique like a rocket-powered sky crane. Among the unknowns will be wind gusts during the spacecraft’s descent, dust storms near the surface and large rocks and loose sand near the landing site.

We’ll find out whether all this effort paid off about 14 minutes after Curiosity either lands or crashes on Mars this coming Monday morning.

Here's a good summary of surface activities and science planned for the Mars Science Laboratory. That Nature article also provides a better measure of the spacecraft's entry and descent velocity that we have: 6 km per second to a standstill. Nature also reports that mission planners estimate there is a 95 percent chance of success, but the problem is the "unknown unknowns" and that the "overall biggest risk is our lack of imagination" NASA JPL is hardly alone on that point:
http://www.nature.com/news/7-minutes-of-terror-1.11089

Thanks for the great interview and story, George. Regarding the sky crane, JPL ran live deployment tests in a hanger, and also accounted for the differences in atmosphere and rocket thrust in digital simulations. Fingers crossed for the final landing! - Tim Nichols, Siemens PLM Software

We've not been able to get a complete rundown on the MSL simulation and testing program, but we do know that there was some actual testing of hardware that most certainly included testing of the rocket motors on the sky crane. Testing of other parts of the entry, descent and landing system are discussed here:
http://nyti.ms/evj2MU
Simulation were widely used for parameters like thermal loads during entry into the Martian atmosphere and to determine how the landing vehicle would handle G loads and severe vibrations.
Cross your fingers that all this preparation will pay off on Monday.

I am interested to learn how this new "Sky Crane" based landing system tested? Was the landing sytem tested by simulating the landing using the software tools (similar to a flight simulator)? Was their any real prototypes of the Sky Crane tested in the laboratory as well?